By dedicating CPUs to Kithara RealTime neither Windows nor other software running in Windows context will have any impact on the real-time behavior of the system.
However, different hardware can have better or worse real-time capabilities and especially configuration options of the BIOS/UEFI can have an impact on the real-time capabilities.

• C1E = Enhanced Power Save Modes of the CPU.
  The power save modes of modern CPUs make the CPUs switch to different sleep modes very rapidly, unpowering different function blocks of the CPU. Waking the CPU from those sleep modes takes time and will introduce latencies.
  For the best real-time experience, all power save modes should be deactivated.
  You will find those options (depending on your BIOS/UEFI) at
  • C1E
  • C-States
  • Deeper C States
• SpeedStep
  The power save options of modern CPUs will make the CPUs switch to lower frequencies on idle. Recovering to higher frequencies on demand takes time and will introduce latencies.
  For the best real-time experience, dynamic frequency changing should be deactived.
  You will find those options (depending on your BIOS/UEFI) at
  • EIST
  • SpeedStep
  • Turbo Boost
  • PowerNow!
  • Cool'n'Quiet
• Legacy USB Support
  From our experience, this option can (depending on UEFI implementation) have bad impact on the real-time capabilities, it should be deactivated.
• Hyper-threading / Simultaneous Multithreading (SMT)
  In most cases, hyper-threading should be deactivated to ensure full access for each 'logical' CPU to the physical CPU resources. See the corresponding note at Dedicating CPUs to Kithara RealTime.
• WBINVD = Assembler instruction for clearing all internal caches.
  This instruction is used, for instance, by Nvidia graphics device drivers. This problem can only be solved by avoiding software utilizing this instruction. For device drivers, only a switch to different hardware with drivers not using this instruction will help.